Power supply system with non-linear capacitance charge-pump

ABSTRACT

One example includes a power supply system. The system includes a switch system comprising a switch that is configured to generate a switching voltage at a switching node in response to an input voltage. The system also includes a non-linear capacitance charge-pump coupled to the switching node and being configured to provide an output current in response to the switching voltage. The output current can have an amplitude that varies non-linearly with respect to an amplitude of the switching voltage. The switch system further includes an output stage configured to generate an output voltage on an output node in response to the output current.

CROSS-REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. § 120, this continuation application claims benefits ofand priority to U.S. patent application Ser. No. 16/012,292, filed onJun. 19, 2018, the entirety of which are hereby incorporated herein byreference.

TECHNICAL FIELD

This disclosure relates generally to electronic systems, and morespecifically to a power supply system with a non-linear capacitancecharge-pump.

BACKGROUND

Power supply circuits can be implemented in a variety of different ways.Examples of power supply circuits include synchronous rectifier powerconverters, asynchronous rectifier power converters, resonant powerconverters, and any of a variety of other types of switching powerconverters. Some power circuits can implement a capacitive charge pumpto control the connection of a supply voltage across a load. Forexample, a variable switching voltage can be provided to the capacitivecharge pump device to charge the capacitive charge pump device in afirst switching phase, such that the capacitive charge pump device isdischarged in a second switching phase to provide the charge to theload.

SUMMARY

One example includes a power supply system. The system includes a switchthat is controlled via a respective switch control signal to generate aswitching voltage at a switching node in response to an input voltage.The system also includes a non-linear capacitance charge-pump coupled tothe switching node and being configured to provide an output current inresponse to the switching voltage. The output current can have anamplitude that varies non-linearly with respect to an amplitude of theswitching voltage. The switch system further includes an output stageconfigured to generate an output voltage on an output node in responseto the output current.

Another example includes a power supply system. The system includes aswitch that is controlled via a respective switch control signal togenerate a switching voltage at a switching node in response to an inputvoltage. The system also includes a non-linear capacitance charge-pumpcoupled to the switching node and being configured to provide an outputcurrent in response to the switching voltage. The output current canhave an amplitude that varies non-linearly with respect to an amplitudeof the switching voltage. The system also includes an output stageconfigured to generate an output voltage on an output node in responseto the output current. The system further includes a switch drive stagethat is configured to provide the switch control signal to therespective switch of the switch system based on the output voltage.

Another example includes a power supply system. The system includes aswitch system comprising a switch that is controlled via a respectiveswitch control signal to generate a switching voltage at a switchingnode in response to an input voltage. The system also includes atransistor device that exhibits a non-linear capacitance coupled to theswitching node and being configured to provide an output current inresponse to the switching voltage. The output current can have anamplitude that varies non-linearly with respect to an amplitude of theswitching voltage. The system further includes an output stageconfigured to generate an output voltage on an output node in responseto the output current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a power supply system.

FIG. 2 illustrates a graph of output charge as a function of voltage.

FIG. 3 illustrates another example of a power supply circuit.

FIG. 4 illustrates another example of a power supply circuit.

FIG. 5 illustrates another example of a power supply circuit.

FIG. 6 illustrates an example of a universal serial bus (USB) powerdelivery system.

DETAILED DESCRIPTION

This disclosure relates generally to electronic systems, and morespecifically to a power supply system with a non-linear capacitancecharge-pump. The power supply system can include a switch system thatincludes at least one switch that is controlled via a respective atleast one switch control signal. The switch system can be configured togenerate a switching voltage at a switching node based on an inputvoltage. For example, the switch system can include at least one switchthat is alternately activated and deactivated and an inductor to conducta current from the input voltage to the switch node. The power supplysystem can also include a non-linear capacitance charge-pump configuredto provide an output current to an output stage in response to theswitching voltage. The output stage is configured to generate an outputvoltage in response to the output current. As an example, the powersupply system can also include a switch drive stage that is configuredto generate the at least one switch control signal based on the outputvoltage.

The output current can have an amplitude that is based on an amplitudeof the switching voltage and the switching frequency of the switch(es)of the switch system. Therefore, because the switching voltage at theswitch node can have an amplitude that varies greatly (e.g., by an orderof magnitude or more), in a typical power supply system, the outputcurrent can have an amplitude that likewise varies greatly. While theoutput stage can include a regulator (e.g., a Zener diode), excessiveamplitude of the output current can be sunk to a low-voltage rail (e.g.,ground), which can result in inefficient waste of power. Therefore, thenon-linear capacitance charge-pump is configured to provide the outputcurrent at amplitudes that vary by much smaller amplitudes in responseto large changes in amplitude of the switching voltage based on having anon-linear capacitance. For example, the non-linear capacitancecharge-pump can be configured as a super-junction (SJ) metal-oxidesemiconductor field-effect transistor (MOSFET). Accordingly, the powersupply system can be operated in a much more power efficient manner thantypical power supply systems.

FIG. 1 illustrates an example of a power supply system 10. The powersupply system 10 can be implemented in any of a variety ofpower-providing applications, such as for a portable electronic device(e.g., for a universal serial bus (USB) power delivery system).

In the example of FIG. 1, the power supply system 10 includes a switchsystem 12, a non-linear capacitance charge-pump 14, and an output stage16. The switch system 12 includes at least one switch 18 that iscontrolled via a respective at least one switch control signal,demonstrated in the example of FIG. 1 as switch control signal(s) SW.The switch system 12 can be configured to generate a switching voltageV_(SW) at a switch node 20 based on an input voltage V_(IN). Forexample, the switch system 12 can include at least one switch 18 that isalternately activated and deactivated and an inductor to conduct acurrent from the input voltage V_(IN) to the switch node 18. As anexample, the switch system 12 can be arranged as a boost switch systemcomprising an inductor interconnecting the input voltage V_(IN) and theswitch node 20, and further comprising a single switch 18interconnecting the switch node 20 and a low-voltage rail.

The non-linear capacitance charge-pump 14 is configured to provide anoutput current I_(OUT) to the output stage 16 in response to theswitching voltage V_(SW). As an example, the non-linear capacitancecharge-pump 14 can exhibit a capacitance that decreases significantly atgreater amplitudes of voltage across the non-linear capacitancecharge-pump 14. For example, the non-linear capacitance charge-pump 14can have a capacitance that decreases by at least one order of magnitudeat a voltage amplitude greater than approximately 25 volts. As oneexample, the non-linear capacitance charge-pump 14 can be configured asa super-junction (SJ) metal-oxide semiconductor field-effect transistor(MOSFET). However, it is to be understood that other types of non-linearcapacitance devices can be implemented instead. For example, the SJMOSFET can be diode-connected (e.g., with a common connection betweensource and gate) between the switch node 20 and the output stage 16. Asdescribed in greater detail herein, the non-linear capacitancecharge-pump 14 can provide the output current I_(OUT) at an amplitudethat can vary by much smaller changes (e.g., non-linearly) in responseto large changes in amplitude of the switching voltage V_(SW) based onhaving a non-linear capacitance.

The output stage 16 is configured to generate an output voltage V_(OUT)in response to the output current I_(OUT). For example, the output stage16 can include a Zener diode to regulate the amplitude of the outputvoltage V_(OUT). As another example, the output stage 16 can include adiode arranged in a forward bias with respect to the output currentI_(OUT) to provide the output current I_(OUT) across an outputcapacitor. The output stage 16 can thus generate the output voltageV_(OUT) that can be provided as a power source, such as to otherelectronic devices.

Additionally, the power supply system 10 further includes can alsoinclude a switch drive stage 22 that is configured to generate theswitch control signal(s) SW based on the output voltage V_(OUT). In theexample of FIG. 1, the switch drive stage 22 receives the output voltageV_(OUT) from the output stage 16 and can generate the switch controlsignal(s) SW to provide the alternate switching of the switch(es) of theswitch system 12. As a result, the output voltage V_(OUT) can operate asfeedback for the switch drive stage 22, despite not necessarily sharinga common low-voltage rail (e.g., ground) connection. For example, theswitch drive stage 22 can generate switch control signal(s) SW based ona pulse-width modulation (PWM) scheme based on the output voltageV_(OUT).

As an example, the switching voltage V_(SW) can have very largeamplitude swings (e.g., one or more orders of magnitude), such as bothgreater than and less than zero. The output voltage V_(OUT) can have anamplitude that is based on an amplitude of the switching voltage V_(SW)and a switching frequency of the switch(es) of the switch system 12 inresponse to the switch control signal(s) SW. As a result, the non-linearcapacitance charge-pump 14 can be configured to mitigate the largeamplitude swings of the output current I_(OUT) based on having anon-linear capacitance.

For example, the non-linear capacitance charge-pump 14 can deliverpulses that are approximately the same at each period of the switchingfrequency to provide, as an example, an approximately 27% amplitudevariation over a variation in amplitude of the switching voltage V_(SW)of approximately 25 to 1. Such operation is demonstrated further in theexample of FIG. 2. FIG. 2 illustrates a graph 40 of output chargeQ_(OSS) as a function of voltage V_(CP). The voltage V_(CP) correspondsto a voltage across the non-linear capacitance charge pump 14. Forexample, the graph 40 can correspond to characteristics of a 600 volt SJMOSFET as part of the non-linear charge pump device 14, such that thevoltage V_(CP) can be a drain-source voltage of the SJ MOSFET. However,other non-linear capacitance devices can be implemented similarlyherein.

In the example of FIG. 2, the graph 40 demonstrates that at amplitudesof the voltage V_(CP) less than approximately 25 volts, that the outputcharge Q_(OSS) is approximately linear with respect to the voltageV_(CP). Therefore, at amplitudes of the voltage V_(CP) less than thepredetermined amplitude of approximately 25 volts, the non-linear chargepump device 14 exhibits a linear capacitance. In the example of FIG. 2,the graph 40 demonstrates that at an amplitude of approximately 25 voltsof the voltage V_(CP), the non-linear charge pump device 14 can storeapproximately 77% of the output charge Q_(OSS). As a result, thenon-linear charge pump device 14 can deliver charge linearly withrespect to variations in the switching voltage V_(SW) of less thanapproximately 25 volts.

However, the graph 40 also demonstrates that at amplitudes of thevoltage V_(CP) greater than the predetermined amplitude of approximately25 volts, that the output charge Q_(OSS) is non-linear with respect tothe voltage V_(CP). Therefore, at amplitudes of the voltage V_(CP)greater than the predetermined amplitude of approximately 25 volts, thenon-linear charge pump device 14 exhibits a non-linear capacitance. As aresult, the non-linear charge pump device 14 can deliver less charge,and thus exhibit less voltage V_(CP), in response to larger variationsin the switching voltage V_(SW).

Therefore, by implementing the non-linear capacitance charge-pump 14 inthe power supply system 10, the power supply system 10 can substantiallymitigate power losses resulting from excess amplitude of the outputcurrent I_(OUT) (e.g., that is regulated via a Zener diode in the outputstage, such as would be the case in the example of a typical powersupply system). Additionally, the power supply system 10 can provide amore simplistic and cost-effective manner of mitigating excessiveamplitude of the output current I_(OUT), such as relative to powersupply systems that implement programmable level-shifting charge pumps(e.g., with multiple capacitance steps). Accordingly, the power supplysystem 10 can be fabricated to provide a simplistic, cost-effective, andpower efficient solution to providing an output voltage V_(OUT) that canlikewise bias the switch drive stage 22, particularly with highvariation in the switching voltage V_(SW).

FIG. 3 illustrates an example of a power supply circuit 50. The powersupply circuit 50 can be implemented in any of a variety ofpower-providing applications, such as for a portable electronic device(e.g., for a USB power delivery system). As an example, the power supplycircuit 50 may provide a structural implementation of the power supplysystem 10 in the example of FIG. 1.

In the example of FIG. 3, the power supply circuit 50 includes a switchsystem 52, a non-linear capacitance charge-pump 54, and an output stage56. The switch system 52 is demonstrated diagrammatically in the exampleof FIG. 3 as a power supply that provides the switching voltage V_(SW)at a switching node 58 (e.g., based on the input voltage V_(IN)). Forexample, the switch system 52 can include at least one switch that iscontrolled via a respective at least one switch control signal SW. Forexample, the switch system 52 can include at least one switch that isalternately activated and deactivated and an inductor to conduct acurrent from the input voltage V_(IN) to the switch node 58.

The non-linear capacitance charge-pump 54 is configured to provide anoutput current I_(OUT) to a node 60 coupled to the output stage 56 inresponse to the switching voltage V_(SW). In the example of FIG. 3, thenon-linear capacitance charge-pump 54 is demonstrated as including avariable capacitor C_(VAR) and a diode D₁. It is to be understood thatany of a variety of different types of non-linear capacitance devicescan be implemented as the variable capacitor C_(VAR). Therefore, similarto as described previously in the example of FIG. 1, the non-linearcapacitance charge-pump 54 can provide the output current I_(OUT) at anamplitude that can vary by much smaller changes (e.g., non-linearly) inresponse to large changes in amplitude of the switching voltage V_(SW)based on having a non-linear capacitance. In the example of FIG. 3, thediode D₁ interconnecting the node 60 and an output node 62, such thatthe diode D₁ provides the output current I_(OUT) to the output node 62in a forward-bias manner.

The output stage 56 is configured to generate an output voltage V_(OUT)at the output node 62 in response to the output current I_(OUT). Theoutput stage 56 includes a diode D₂ that is arranged between the node 60and the low-voltage rail (e.g., ground) in a reverse-bias manner. Theoutput stage 56 further includes a Zener diode D3 that is configured toregulate the amplitude of the output voltage V_(OUT) by allowing anexcessive amplitude of the output current I_(OUT) to flow to thelow-voltage rail. In the example of FIG. 3, the output current I_(OUT)is provided across an output capacitor C_(OUT) to provide the outputvoltage V_(OUT) at the output node 62. As an example, the output voltageV_(OUT) can be provided as a power source, such as to other electronicdevices, and can also be provided as a feedback source to an associatedswitch drive stage (e.g., the switch drive stage 22 in the example ofFIG. 1).

Similar to as described previously, the switching voltage V_(SW) canhave a very large amplitude swing (e.g., one or more orders ofmagnitude), such as both greater than and less than zero. The outputvoltage V_(OUT) can have an amplitude that is based on an amplitude ofthe switching voltage V_(SW) and a switching frequency of the switch(es)of the switch system 52. Advantageously, the non-linear capacitancecharge-pump 54 can be configured to mitigate the large amplitude swingsof the output current I_(OUT) based on having a non-linear capacitance.

For example, the output current I_(OUT) is generated based on thecapacitance of the non-linear capacitance charge pump 54 and theamplitude of the switching voltage V_(SW), and is proportional to theswitching frequency of the switch system 52. Therefore, in response to ahigh-dynamic range of the switching voltage V_(SW), the non-linearcapacitance of the non-linear capacitance charge pump 54, the outputcurrent I_(OUT) can have an amplitude that exhibits a non-linearresponse at amplitudes of the switching voltage V_(SW) that are greaterthan a predetermined amplitude. For example, for a linear capacitance ofa typical charge pump, the output current I_(OUT) would increase inamplitude linearly with the amplitude of the switching voltage V_(SW),which could result in inefficient power losses (e.g., through areverse-bias breakdown of an associated Zener diode). However, by takingadvantage of a non-linear capacitance, the non-linear capacitance chargepump 54 can deliver charge that varies little in response to largevariations of the switching voltage V_(SW) (e.g., approximately 27%amplitude variation of the output current I_(OUT) over a variation inamplitude of the switching voltage V_(SW) of approximately 25 to 1).Accordingly, the power supply circuit 50 can be fabricated to provide asimplistic, cost-effective, and power efficient solution to providing anoutput voltage V_(OUT) based on a potentially high variation in theamplitude of the switching voltage V_(SW).

FIG. 4 illustrates an example of a power supply circuit 100. The powersupply circuit 100 can be implemented in any of a variety ofpower-providing applications, such as for a portable electronic device(e.g., for a USB power delivery system). As an example, the power supplycircuit 100 can correspond to at least a portion of the power supplysystem 10 in the example of FIG. 1.

In the example of FIG. 4, the power supply circuit 100 includes a switchsystem 102, a non-linear capacitance charge-pump 104, and an outputstage 106. The switch system 102 is demonstrated diagrammatically in theexample of FIG. 4 as a power supply that provides the switching voltageV_(SW) at a switching node 108 (e.g., based on the input voltageV_(IN)). For example, the switch system 102 can include at least oneswitch that is controlled via a respective at least one switch controlsignal SW. For example, the switch system 102 can include at least oneswitch that is alternately activated and deactivated and an inductor toconduct a current from the input voltage V_(IN) to the switch node 108.

The non-linear capacitance charge-pump 104 is configured to provide anoutput current I_(OUT) to a node 110 coupled to the output stage 106 inresponse to the switching voltage V_(SW). In the example of FIG. 4, thenon-linear capacitance charge-pump 104 is demonstrated as including anN-channel transistor device N₁, which can be configured as asuper-junction (SJ) MOSFET, and a diode D₁. The N-FET N₁ is demonstratedin the example of FIG. 4 as being diode-connected, such that the gateand source of the N-FET N₁ are each coupled together at the node 110.Because an SJ MOSFET exhibits a non-linear parasitic capacitance acrossthe drain/source connection while activated (e.g., in a linear mode orsaturation mode of operation of the N-FET N₁), the non-linearcapacitance charge-pump 104 can provide the output current I_(OUT) at anamplitude that can vary by much smaller changes (e.g., non-linearly) inresponse to large changes in amplitude of the switching voltage V_(SW)based on having a non-linear capacitance. In the example of FIG. 4, thediode D₁ interconnecting the node 110 and an output node 112, such thatthe diode D₁ provides the output current I_(OUT) to the output node 112in a forward-bias manner.

The output stage 106 is configured to generate an output voltage V_(OUT)at an output node 112 in response to the output current I_(OUT). Theoutput stage 106 includes a diode D₂ that is arranged between the node110 and the low-voltage rail (e.g., ground) in a reverse-bias manner.The output stage 106 further includes a Zener diode D3 that isconfigured to regulate the amplitude of the output voltage V_(OUT) byallowing an excessive amplitude of the output current I_(OUT) to flow tothe low-voltage rail. In the example of FIG. 4, the output currentI_(OUT) is provided across an output capacitor C_(OUT) to provide theoutput voltage V_(OUT) at the output node 112. As an example, the outputvoltage V_(OUT) can be provided as a power source, such as to otherelectronic devices, and can also be provided as a power source to anassociated switch drive stage (e.g., the switch drive stage 22 in theexample of FIG. 1).

Similar to as described previously, the switching voltage V_(SW) canhave a very large amplitude swing (e.g., one or more orders ofmagnitude), such as both greater than and less than zero. Because theoutput voltage V_(OUT) can have an amplitude that is based on anamplitude of the switching voltage V_(SW) and a switching frequency ofthe switch(es) of the switch system 102, the non-linear capacitancecharge-pump 104 can be configured to mitigate the large amplitude swingsof the output current I_(OUT) based on having a non-linear capacitance,similar to as described previously in the example of FIG. 3.Accordingly, the power supply circuit 100 can be fabricated to provide asimplistic, cost-effective, and power efficient solution to providing anoutput voltage V_(OUT) based on a potentially high variation in theamplitude of the switching voltage V_(SW).

FIG. 5 illustrates an example of a power supply circuit 150. The powersupply circuit 150 can be implemented in any of a variety ofpower-providing applications, such as for a portable electronic device(e.g., for a USB power delivery system). As an example, the power supplycircuit 150 can correspond to at least a portion of the power supplysystem 10 in the example of FIG. 1.

In the example of FIG. 5, the power supply circuit 150 includes a switchsystem 152, a non-linear capacitance charge-pump 154, and an outputstage 156. The switch system 152 is demonstrated diagrammatically in theexample of FIG. 5 as a power supply that provides the switching voltageV_(SW) at a switch node 158 (e.g., based on the input voltage V_(IN)).For example, the switch system 152 can include at least one switch thatis controlled via a respective at least one switch control signal SW.For example, the switch system 152 can include at least one switch thatis alternately activated and deactivated and an inductor to conduct acurrent from the input voltage V_(IN) to the switch node 158.

The non-linear capacitance charge-pump 154 is configured to provide anoutput current I_(OUT) to a node 160 coupled to the output stage 156 inresponse to the switching voltage V_(SW). In the example of FIG. 5, thenon-linear capacitance charge-pump 154 is demonstrated as an N-channeltransistor device N₁, which can be configured as a super-junction (SJ)MOSFET, and a diode D₁. The N-FET N₁ is demonstrated in the example ofFIG. 5 as being diode-connected, such that the gate and source of theN-FET N₁ are each coupled together at the node 160. Because an SJ MOSFETexhibits a non-linear parasitic capacitance across the drain/sourceconnection while activated (e.g., in a linear mode or saturation mode ofoperation of the N-FET N₁), the non-linear capacitance charge-pump 154can provide the output current I_(OUT) at an amplitude that can vary bymuch smaller changes (e.g., non-linearly) in response to large changesin amplitude of the switching voltage V_(SW) based on having anon-linear capacitance. In the example of FIG. 5, the diode D₁interconnecting the node 160 and an output node 162, such that the diodeD₁ provides the output current I_(OUT) to the output node 162 in aforward-bias manner.

The output stage 156 is configured to generate an output voltage V_(OUT)at an output node 162 in response to the output current I_(OUT). Theoutput stage 156 includes a diode D₂ that is arranged between the node160 and the low-voltage rail (e.g., ground) in a reverse-bias manner. Inthe example of FIG. 5, the output current I_(OUT) is provided across anoutput capacitor C_(OUT) to provide the output voltage V_(OUT) at theoutput node 162. As an example, the output voltage V_(OUT) can beprovided as a power source, such as to other electronic devices, and canalso be provided as a power source to an associated switch drive stage(e.g., the switch drive stage 22 in the example of FIG. 1).

The output stage 156 further includes a Zener diode D₃ and a resistor R₁that are arranged to regulate the amplitude of the output voltageV_(OUT). In the example of FIG. 5, the Zener diode D₃ and the resistorR₁ are arranged as a voltage-divider between the output node 162 and thelow-voltage rail, such that a control node 164 between the Zener diodeD3 and the resistor R1 controls a gate of an N-channel transistor deviceN₂ that forms part of the output stage 156 Therefore, the N-FET N₂ canregulate the amplitude of the output current I_(OUT). For example, inresponse to the amplitude of the output current I_(OUT) beingsufficiently high to flow through the Zener diode, an activation voltageis provided at the control node 164, across the resistor R1, to activatethe N-FET N₂. Accordingly, the N-FET N₂ can sink a portion of the outputcurrent I_(OUT) to the low-voltage rail. While the example of FIG. 5demonstrates that the regulator device is the N-FET N₂, it is to beunderstood that a variety of other types of regulator devices, such asincluding a comparator, can instead be implemented to regulate theamplitude of the output current I_(OUT).

Similar to as described previously, the switching voltage V_(SW) canhave a very large amplitude swing (e.g., one or more orders ofmagnitude), such as both greater than and less than zero. Because theoutput voltage V_(OUT) can have an amplitude that is based on anamplitude of the switching voltage V_(SW) and a switching frequency ofthe switch(es) of the switch system 152, the non-linear capacitancecharge-pump 154 can be configured to mitigate the large amplitude swingsof the output current I_(OUT) based on having a non-linear capacitance,similar to as described previously in the example of FIG. 3.Accordingly, the power supply circuit 150 can be fabricated to provide asimplistic, cost-effective, and power efficient solution to providing anoutput voltage V_(OUT) based on a potentially high variation in theamplitude of the switching voltage V_(SW).

FIG. 6 illustrates an example of a USB power delivery system 200. TheUSB power delivery system 200 can correspond to any of a variety of USBpower supplies to provide DC power to, for example, a portableelectronic device. For example, the USB power delivery system 200 can beincluded in a USB plug-in adapter that can be configured to transmitdata and power to a portable electronic device. The USB power deliverysystem 200 includes a power converter 202 and a power supply system 204.In the example of FIG. 6, the USB power delivery system 200 isdemonstrating as receiving a power voltage V_(PWR). As an example, thepower converter 202 can be configured as an AC-to-DC converter, suchthat the power voltage V_(PWR) can be an AC utility power voltage (e.g.,120 VAC/60 Hz) that can be received via a power outlet. Alternatively,the power voltage V_(PWR) can be a DC voltage, such that the powerconverter 202 can be a step-down power converter. The power converter202 is configured to provide a DC input voltage V_(IN) to the powersupply system 204.

The power supply system 204 can be configured as a DC-DC power converterconfigured to generate a DC output voltage V_(OUT) based on the DC inputvoltage V_(IN). For example, the power supply system 204 can correspondto the power supply system 10 in the example of FIG. 1, or any of thepower supply circuits 50, 100, or 150 in the respective examples ofFIGS. 2-4. Therefore, the power supply system 204 can include anon-linear charge pump that is configured to provide an output currentat amplitudes that vary by much smaller amplitudes in response to largechanges in amplitude of a respective switching voltage based on having anon-linear capacitance, similar to as described previously. For example,the non-linear capacitance charge-pump can be configured as an SJMOSFET. Accordingly, the power supply system can be operated in a muchmore power efficient manner than typical power supply systems.

What have been described above are examples of the present invention. Itis, of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the presentinvention, but one of ordinary skill in the art will recognize that manyfurther combinations and permutations of the present invention arepossible. Accordingly, the present invention is intended to embrace allsuch alterations, modifications and variations that fall within thespirit and scope of the appended claims. Additionally, where thedisclosure or claims recite “a,” “an,” “a first,” or “another” element,or the equivalent thereof, it should be interpreted to include one ormore than one such element, neither requiring nor excluding two or moresuch elements. As used herein, the term “includes” means includes butnot limited to, and the term “including” means including but not limitedto. The term “based on” means based at least in part on.

What is claimed is:
 1. A power supply comprising: a switch systemincluding a switch node; a charge pump circuit including: a variablecapacitor that includes a transistor having a drain terminal coupled tothe switch node and a source terminal coupled to a gate terminal; and adiode having an anode coupled to the source terminal of the transistor,and a cathode coupled to an output terminal; and an output stage coupledto the charge pump circuit, and configured to generate an output voltageat the output terminal in response to a current from the second terminalto the anode.
 2. The power supply of claim 1, wherein the transistor isa first transistor, and the output stage includes: a second transistorhaving a drain coupled to the source of the first transistor, a sourcecoupled to a ground terminal, and a gate; a Zener diode having an anodecoupled to the gate of the second transistor, and a cathode coupled tothe output terminal; and a resistor having a first end coupled to theanode of the Zener diode, and a second end coupled to the groundterminal.
 3. The power supply of claim 2, wherein the first transistorincludes a first n-channel transistor, and the second transistorincludes a second n-channel transistor.
 4. The power supply of claim 1,wherein the diode is a first diode, and the output stage includes: asecond diode having an anode coupled to a ground terminal, and a cathodecoupled to the source terminal of the first transistor; and a Zenerdiode having an anode coupled to the ground terminal, and a cathodecoupled to the output terminal.
 5. The power supply of claim 4, whereinthe output stage includes an output capacitor coupled between the outputterminal and the ground terminal.
 6. The power supply of claim 1,further comprising: a switch drive coupled to the output terminal, andconfigured to generate a drive signal for driving the switch system,wherein the drive signal is responsive to the output voltage.
 7. Thepower supply of claim 6, wherein the switch system includes a switchcoupled between an input terminal and the switch node, the switch havinga control coupled to receive the drive signal.
 8. A universal serial bus(USB) power delivery (PD) device comprising: a switch system including aswitch node; a charge pump circuit including: a variable capacitorhaving a first terminal coupled to the switch node, and a secondterminal; and a diode having an anode coupled to the second terminal ofthe variable capacitor, and a cathode coupled to an output terminal; andan output stage coupled to the charge pump circuit, and configured togenerate an output voltage at the output terminal in response to acurrent from the second terminal to the anode.
 9. The USB PD device ofclaim 8, wherein the variable capacitor includes a transistor having adrain as the first terminal, a source as the second terminal, and a gatecoupled to the source.
 10. The USB PD device of claim 9, wherein thetransistor is a first transistor, and the output stage includes: asecond transistor having a drain coupled to the source of the firsttransistor, a source coupled to a ground terminal, and a gate; a Zenerdiode having an anode coupled to the gate of the second transistor, anda cathode coupled to the output terminal; and a resistor having a firstend coupled to the anode of the Zener diode, and a second end coupled tothe ground terminal.
 11. The USB PD device of claim 10, wherein thefirst transistor includes a first n-channel transistor, and the secondtransistor includes a second n-channel transistor.
 12. The USB PD deviceof claim 8, wherein the diode is a first diode, and the output stageincludes: a second diode having an anode coupled to a ground terminal,and a cathode coupled to the second terminal of the variable capacitor;and a Zener diode having an anode coupled to the ground terminal, and acathode coupled to the output terminal.
 13. The USB PD device of claim12, wherein the output stage includes an output capacitor coupledbetween the output terminal and the ground terminal.
 14. The USB PDdevice of claim 8, further comprising: a switch drive coupled to theoutput terminal, and configured to generate a drive signal for drivingthe switch system, wherein the drive signal is responsive to the outputvoltage.
 15. The USB PD device of claim 14, wherein the switch systemincludes a switch coupled between an input terminal and the switch node,the switch having a control coupled to receive the drive signal.
 16. Apower supply comprising: a switch system including a switch node; acharge pump circuit including: a first transistor having a drain coupledto the switch node, a source, and a gate coupled to the source; and adiode having an anode coupled to the source of the first transistor, anda cathode coupled to an output terminal; and an output stage including:a second transistor having a drain coupled to the source of the firsttransistor, a source coupled to a ground terminal, and a gate; a Zenerdiode having an anode coupled to the gate of the second transistor, anda cathode coupled to the output terminal; and a resistor having a firstend coupled to the anode of the Zener diode, and a second end coupled tothe ground terminal.
 17. The power supply of claim 16, wherein the firsttransistor includes a first n-channel transistor, and the secondtransistor includes a second n-channel transistor.
 18. The power supplyof claim 16, further comprising: a switch drive coupled to the outputterminal, and configured to generate a drive signal for driving theswitch system, wherein the drive signal is responsive to an outputvoltage received from the output terminal.
 19. The power supply of claim18, wherein the switch system includes a switch coupled between an inputterminal and the switch node, the switch having a control coupled toreceive the drive signal.